'American Horror Story' Season 5 Spoilers: Helena Mattsson Joins Cast

Actress Helena Mattsson is joining the cast of "American Horror Story" in its fifth season.

Best known for her roles in "Desperate Housewives," "Nikita," and "Mistresses," as well as "Fargo," and "666 Park Avenue," the Swedish addition to the horror franchise seems to add excitement to the already excited audience.

Her character is still a secret as of the moment. It seems that she will likely bump into old characters in the franchise as creator Ryan Murphy went on record, saying "characters from previous seasons will come back and check into the hotel," according to a report from the Inquisitr.

And though Mattsson's character is still unknown, her character's name has been released already. According to her, the character she will be playing in "American Horror Story: Hotel" does have a name already: Agnetha.

"Another day at work. Getting ready to film some scary stuff.. #thatsallicansay #americanhorrorstory" tweets Mattsson about the series she just joined.

Reports say that so far, she will only star in one episode; episode 1 (entitled "Checking In"). While it doesn't tell fans how long she will stay in the series, it does reveal how the show's details are kept in secret. The filming for the show has just begun this month, and the airing will be this coming October.

Also starring in the fifth season of "American Horror Story" are Sarah Paulson (as hypodermic Sally), Angela Bassett (Ramona), Kathy Bates (Iris), Wes Bentley, Matt Bomer (Donovan), Andy Martinez Jr. (Officer Romero), Evan Peters (Mr. March),  Lady Gaga (who posted a picture of the blood-soaked script, according to the International Business Times), Max Greenfield, Cheyenne Jackson, Denis O'Hare, Chloë Sevigny, and Finn Wittrock.

It was also announced that Richard Jones will join the cast as Detective Hahn, a homicide detective.

The fifth installment of the stomach-churning franchise will revolve around a hotel where people check in, and experience a lot of things.

Creator Ryan Murphy gives the synopsis for "American Horror Story: Hotel".

"It's based in the hotel in horror movies and horror tropes. We've researched several real-live hotels in downtown LA where absolutely horrifying things happened...

When you check into a hotel, there are certain things beyond your control. Other people have the keys to your room; they can come in there. You're not exactly safe, it's a very unsettling idea."

"American Horror Story: Hotel" will premiere on FX this fall.